Late blight is a gas-borne fungal disease that mainly invades leaves, stems, and tubers. The main symptom of the leaves is that, first of all, a greenish hot green spot begins from the tip of the leaf, and a green halo surrounds the spot. When the humidity is high, the lesion quickly enlarges and a white floc-like layer, the pathogen, appears on the back of the leaves. When a central diseased plant occurs in the field, if it is not controlled in time, and the humidity is high, it will quickly spread to all fields with the air flow. Symptoms on the tuber are first light brown lesions, the lesions are slightly sunken, and when the humidity is high, white flocculosis is produced on the lesions. Infected by bacteria, tuber will appear rotten. If the soil moisture is small, the lesions are brownish and dry. After the general plant leaves are affected, the tubers will also be infected.
In the field management, observe whether the above symptoms are present in the leaves. If there is a central diseased plant, it is necessary to pay close attention to the use of chemical control. 72.2% of urea manganese zinc (Kelu) wettable powder can be used 600-800 times, 77% copper hydroxide (also known as chloramphenicol) can be 500-1000 times wettable powder, can also be 1:1:200 times Bordeaux fluid or 50% metalaxyl manganese zinc is treated 800-1000 times.
In particular, if the incidence of disease in the field is heavy, the upper diseased leaves should be cut off 10 days before the harvest of the seed potato so as not to invade the potato stalks; the harvested seed potatoes must be air-dried and the diseased tubers must be strictly removed. In order to prevent the storage period caused by rotten pit and the second year to bring the bacteria to the field.
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